A necklace has 27 pearls. The biggest pearl in the middle is

>For every pearl that you move away from the middle pearl, the diameter decreases with 5%.

what do you mean? 100% - 95% - 90% - 85% etc of the middle pearl or always 95% of the previous pearl?

and what exactly do you need help with? apart from the ambiguity it's a pretty simple task. even if you don't clue into it either being an arithmetic or geometric series you can always just calculate each value and add them up.

>>125094
58.4806cm

>>125098
5% smaller than the previous pearl

Last pearl is 3*(0.95^13), roughly 1.54 cm

>>125129
This.

>>125094
You have a series where d=3*(.95^n) where n is the position and d is the diameter. Integrate that from 0 to 13, multiply by 2, and then add the initial diameter for your starting position. That should work.
I got 21.9755cm using this method.

>>125161
this sounds right, except it wouldnt be 0-13, it would be 1-13 (n=0 starts at the central pearl, which if we included in this way would be counted twice, and then an additional time via your method) so instead it would be that sum from 1-13, doubled, and then having the initial diameter added.